Optical sensors for detecting relative motion and/or position and methods and systems for using such optical sensors

ABSTRACT

An optical sensor, according to an embodiment of the present invention, includes a photodetector region and a plurality of slats over the photodetector region. In an embodiment, the slats are made of an opaque polymer material, such as an opaque photoresist. In an embodiment, the slats are angled relative to a surface of the photodetector region.

PRIORITY CLAIMS

This application is a continuation of U.S. patent application Ser. No.14/102,245, filed Dec. 10, 2014, which is a divisional of U.S. patentapplication Ser. No. 13/584,623, filed Aug. 13, 2012, which claimspriority under 35 U.S.C. 119(e) to U.S. Provisional Patent ApplicationNo. 61/666,666, filed Jun. 29, 2012.

U.S. patent application Ser. No. 13/584,623 is a continuation-in-part(CIP) of U.S. patent application Ser. No. 13/466,867, filed May 8, 2012,which claims priority under 35 U.S.C. 119(e) to U.S. Provisional PatentApplication No. 61/496,336, filed Jun. 13, 2011, and U.S. ProvisionalPatent Application No. 61/534,314, filed Sep. 23, 2011.

Priority is claimed to each of the above applications.

Each of the above applications is incorporated herein by reference.

BACKGROUND

Technologies, such as touch sensitive screens, have allowed users toprovide inputs to electronic devices, such as mobile phones and tabletcomputers, without requiring the use of a mouse and/or a keyboard.Examples of touch sensitive screens include capacitive sensors, pressuresensitive membranes, beam break techniques with circumferential lightsources and sensors, and acoustic ranging techniques. However, thesetypes of interfaces can only provide information to the device regardingthe touch event, itself, and thus can be limited in application. Inaddition, such types of interfaces can be limited in the number of touchevents that can be handled over a given amount of time, and can be proneto interpret unintended contacts, such as from a shirt cuff or palm, astouch events.

As an alternative to touch sensitive screens, optical motion and/orgesture recognition sensors have been developed, which can be used torecognize different motions of an object (e.g., a persons finger) withinthe sense region of the sensor. Typically, such optical sensors rely onmultiple spatially dispersed light sources, multiple spatially dispersedlight detectors, or both, to enable them to distinguish between motionin one or two directions. For example, one existing sensor includes aphotodetector that is flanked on both sides by infrared light emittingdiodes (IR-LEDs) spaced several tens of millimeters away from thephotodetector to provide sufficient angular resolution, and a thirdIR-LED that is spaced several tens of millimeters away from thephotodetector in a direction orthogonal to the line of the first twoIR-LEDs and the photodetector. The IR-LEDs are pulsed one at a time,sequentially, such that the detected reflected light signals can beassociated with the correct light source and its known location relativeto the photodetector. From the detected reflected light pulses, agesture recognition algorithm determines the direction and velocity of atarget object, such as a user's finger.

A disadvantage of the exemplary configuration described above is that itrequires at least three spatially dispersed light sources to detectmovement in two directions (e.g., the x-direction and the y-direction),or at least two spatially dispersed light sources to detect movement inone direction (e.g., only the x-direction). Accordingly, such aconfiguration requires a relatively large footprint because of thespatial distances required between the light sources and the opticalsensor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates a perspective view of an optical sensor including aphotodetector region above which are located parallel slats.

FIG. 1B illustrates a perspective view of an optical sensor including aphotodetector region above which are located parallel 1 slats that areorthogonal to the slats in FIG. 1A.

FIG. 1C illustrates a perspective view of an optical sensor including aphotodetector region above which are located crisscrossing slats.

FIG. 1D illustrates how the optical sensors of FIGS. 1A, 1B and 1C canbe configured with a light source to detect light originating from thelight source that has been reflected off of an object moving relative tothe sensors.

FIG. 2A is a top view of the optical sensor of FIG. 1A.

FIG. 2B is a top view of the optical sensor of FIG. 1B.

FIG. 2C is a top view of the optical sensor of FIG. 1C.

FIGS. 3A and 4A are exemplary current versus time responses for theoptical sensor of FIGS. 1A and 2A.

FIGS. 3B and 4B are exemplary current versus time responses for theoptical sensor of FIGS. 1B and 2B.

FIGS. 3C and 4C are exemplary current versus time responses for theoptical sensor of FIGS. 1C and 2C.

FIG. 5A illustrates how the slats shown in earlier FIGS. can be made ofmetal during BEOL metallization process steps.

FIG. 5B is similar to FIG. 5A, but illustrates how a filter can beformed in a trench under the slats.

FIGS. 6A and 6B are side views of optical sensors according to furtherembodiments of the present invention.

FIG. 7 illustrates how the slanted slats shown in FIGS. 6A and 6B can bemade of metal during BEOL metallization process steps.

FIG. 8 is a high level block diagram of a system according to anembodiment of the present invention.

FIG. 9 is a high level block diagram that is used to describe methodsaccording to various embodiments of the present invention.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings that form a part hereof, and in which is shown byway of illustration specific illustrative embodiments. It is to beunderstood that other embodiments may be utilized and that mechanicaland electrical changes may be made. The following detailed descriptionis, therefore, not to be taken in a limiting sense. In the descriptionthat follows, like numerals or reference designators will be used torefer to like parts or elements throughout. In addition, the first digitof a reference number identifies the drawing in which the referencenumber first appears.

FIG. 1A illustrates a perspective view of an optical sensor 102A,according to an embodiment of the present invention. The optical sensor102A includes a photodetector (PD) region 104A above which are locatedparallel slats 112A. FIG. 1B illustrates a perspective view of anoptical sensor 102B including a PD region 104B above which are locatedparallel slats 112B, which are orthogonal to the slats 112A in FIG. 1A.FIG. 1C illustrates a perspective view of an optical sensor 102Cincluding a PD region 104C above which are located crisscrossing slats112C. FIGS. 2A, 2B and 2C illustrate, respectively, top views of theoptical sensors 102A, 102B and 102C. The sensors 102A, 102B and 102C canbe collectively or individual referred to as sensor(s) 102, the PDregions 104A, 104B and 104C can collectively or individually be referredto as PD region(s) 104, and the slats 112A, 112B and 112C can becollectively or individually referred to as slat(s) 112.

Each PD region 104, which is formed in a semiconductor wafer substrate106, can be, e.g., a photodiode, photoresistor, a photovoltaic cell, aphototransistor, or a charge-coupled device (CCD), but is not limitedthereto, and can be used to produce a current or voltage indicative ofdetected light. Unless stated otherwise, for consistency, it will beassumed that each PD region 104 is a photodiode that produces a currentindicative of detected light. In accordance with specific embodiments,all of the optical sensors 102A, 102B and 102C are fabricated in a samewafer substrate 106, and thus, on a same die.

In accordance with specific embodiments of the present invention, theslats 112 are made of metal and are formed during back-end-of-line(BEOL) metallization process steps. Additional details of how metalslats can be formed are discussed below with reference to FIGS. 5A and5B. Alternatively, the slats 112 can be made of an opaque polymermaterial, e.g., such as an opaque (e.g., black or green) photoresist.

In accordance with specific embodiments, one or more filters is/areformed above and/or below the slats 112. For example, an inorganicdielectric optical filter that rejects infrared (IR) light, which canalso be referred to as an IR-cut filter, can be formed below the slats112 in a trench, as described below with reference to 5B. Alternatively,such an inorganic dielectric optical filter can be designed to rejectvisible light and pass IR-light. The design of the filter(s) will dependon the system in which optical sensor is be used. In other embodiments,the filter(s) are deposited and thereby formed above the slats 112.Additionally, or alternatively, one or more organic color filter(s) canbe used.

In accordance with certain embodiments of the present invention, theoptical sensors 102A and 102B are collectively used to detect motion ofan object (or a light source) relative to the sensors 102. The opticalsensor 102C is used to detect when an object (or a light source) isdirectly over the sensor 102C. More specifically, in accordance withcertain embodiments of the present invention, the current versus timeresponses of the optical sensors 102A and 102B are used to detectwhether an object is moving in a first direction (e.g., left-to-right)relative the sensors, or in a second direction (e.g., fore-to-aft)relative to the sensors that is generally orthogonal to the firstdirection. The current versus time response of the optical sensor 102Cis used to detect when an object (or a light source) is substantiallydirectly over the sensor 102C. Exemplary current versus time responsesfor the optical sensors 102A, 102B and 102C are illustrated anddescribed below with reference to FIGS. 3A-3C and 4A-4C.

The sensors 102 can be used in various different manners. For example,referring to FIG. 1D, the sensors 102 can be used to detect lighttransmitted by an adjacent light source 122 that has reflected off of anobject 132. For another example, rather than detecting reflected light,the sensors 102 can detect light transmitted from a light source that isgenerally in line with the sensors 102, as well as the blocking of suchlight. In accordance with certain embodiments, the light source 122 canbe, e.g., an infrared (IR) light emitting diode (LED) or laser diode.However, other types of light sources and alternative wavelengths oflight can be used. These embodiments can be better understood withreferences to FIGS. 3A-3C and 4A-4C described below. If filter(s) is/areused with the configuration shown in FIG. 1D, the filter(s) should passlight of the wavelengths produced by the light source 122 (e.g., IRwavelengths) and reject light of other wavelengths (e.g., visiblewavelengths).

Assuming the configuration shown in FIG. 1D (where the sensors 102A,102B and 102C are used with the light source 122), FIGS. 3A, 3B and 3Cillustrate exemplary current versus time responses, respectively, forthe optical sensors 102A, 102B and 102C when the object 132 moves fromleft-to-right over the sensors 102. The responses in FIGS. 3A and 3B canbe compared to one another in order to determine whether the object 132is moving left-to-right, or fore-to-aft, over the sensors 102A and 102B.For example, the responses can be integrated and results of theintegrations can be compared to one another (e.g., using a comparator,or using subtraction). The responses can be compared to one another inthe analog domain, or the responses can be converted to the digitaldomain using analog-to-digital converters (ADCs) and compared in thedigital domain.

Referring to FIGS. 3A and 3B, the integration of the response in FIG. 3Bwould be greater than the integration of the response in FIG. 3A, whichis indicative of the object 132 moving left-to-right (or more generally,in the x-direction), as opposed to fore-to-aft (or more generally, inthe y-direction). Referring to the response in FIG. 3A, because of theorientation of the slats 112A of the sensor 102A relative to the lightreflecting from the object 132, the current response increases as theobject approaches the sensor 102A from left, peaks when the object 132is overhead, and decreases as the object moves to the right of thesensor 102A. Referring to the response in FIG. 3B, because of theorientation of the slats 112B of the sensor 102B relative to the lightreflecting from the object 132, the current response stays moreconsistent as the object approaches the sensor 102B from left, movesoverhead, and moves to the right of the sensor 102B. Referring to theresponse in FIG. 3C, do to the crisscross orientation of the slats 112C,there is a much more narrow response that peaks when the object is abovethe sensor 102C.

Similar responses to those illustrated in FIGS. 3A, 3B and 3C wouldoccur if the sensors 102A, 102B and 102C were in line with a lightsource, and thus, the sensors 102 detected light transmitted directlyfrom the light source (as opposed to reflected light). Morespecifically, the responses in FIGS. 3A and 3B would correspond to thelight source moving left-to-right relative to the sensors 102A and 102B,respectively, or the sensors 102A and 102B moving left-to-right relativeto the light source. Such a configuration can be used, e.g., toautomatically align components of industrial equipment, or to monitorthe motion of a game controller, or the like. For example, the sensors102 can be attached to a first element of a system, and a light sourcecan be attached to a second element of the system that is generallyacross from the first element. In this manner, alignment and/or motionof one of the elements relatively to the other can be detected and usedas feedback to adjust one of the elements, or to control a furtherelement.

Assuming the configuration shown in FIG. 1D (where the sensors 102A,102B and 102C are used with the light source 122), FIGS. 4A, 4B and 4Cillustrate exemplary current versus time responses, respectively, forthe optical sensors 102A, 102B and 102C when the object 132 moves fromfore-to-aft over the sensors 102. The responses in FIGS. 4A and 4B canbe compared to one another in order to determine whether the object 132is moving left-to-right, or fore-to-aft, relative to the sensors 102Aand 102B.

Referring to FIGS. 4A and 4B, the integration of the response in FIG. 4Awould be greater than the integration of the response in FIG. 4B, whichis indicative of the object 132 moving fore-to-aft (or more generally,in the y-direction), as opposed to left-to-right (or more generally, inthe x-direction). Referring to the response in FIG. 4A, because of theorientation of the slats 112A of the sensor 102A relative to the lightreflecting from the object 132, the current response stays relativelyconsistent as the object moves fore-to-aft over the sensor 102A.Referring to the response in FIG. 4B, because of the orientation of theslats 112B of the sensor 102B relative to the light reflecting from theobject 132, the current response increases as the object approaches thesensor 102A from back, peaks when it's overhead, and decreases as theobject moves forward past the sensor 102B. Referring to the response inFIG. 4C, do to the crisscross orientation of the slats 112C, there is amuch more narrow response that peaks when the object is above the sensor102C.

Similar responses to those illustrated in FIGS. 4A, 4B and 4C wouldoccur if the sensors 102A, 102B and 102C were in line with a lightsource, and thus, the sensors 102 detected light transmitted directlyfrom the light source (as opposed to reflected light). Morespecifically, the responses in FIGS. 4A and 4B would correspond,respectively, to a light source moving fore-to-aft relative to thesensors 102A and 102B, or the sensors 102A and 102B moving fore-to-aftrelative to the light source.

If there is a desire to distinguish left-to-right movement fromright-to-left movement, then two of the sensors 102A can be used, e.g.,one on the left, and the other one on the right. Here it would beexpected that the one of the two sensors 102A closer to a moving object(that reflects light) or closer to a moving light source would producean earlier and greater response than the one of the sensors 102A furtherfrom the object or moving light source. Similarly, if there is a desireto distinguish fore-to-aft movement from aft-to-fore movement, two ofthe sensors 102B can be used, with one in the forefront of the other. Inother words, pairs of each type of the sensors 102A and 102B can used toprovide stereoscopic capabilities. If there is a desire to distinguishbetween an object being located overhead relative to multiple differentpositions, then multiple sensors 102C can be spaced apart and used.

Reference will now be made to FIG. 5A to explain in some more detail howthe slats 112 can be made of metal during BEOL metallization processsteps. Referring to FIG. 5A, the stats 112 are shown as being formedfrom a plurality of metal layers 532, which are connected in a stackedconfiguration with a plurality of metal columns 534, such as vias,contacts, or plugs (e.g., Tungsten or Copper plugs).

Each metal layer can include a stack of metal layers, including, e.g.,an adhesion layer (also known as a barrier layer) at the bottom (made ofTi and or TiN), a bulk conductive layer in the middle, and ananti-reflective coating (ARC) layer on the top. The adhesion layer canbe, e.g., made of Titanium (Ti) and/or Titanium Nitride (TiN), but isnot limited thereto. The bulk layer can be, e.g., made of Aluminum (Al),Copper (Cu) and/or Aluminum Copper (AlCu), but is not limited thereto.The ARC layer can, e.g., be made of TiN, but is not limited thereto.Each column (e.g., Tungsten or Cupper) plug can similarly include anadhesion layer at its bottom. If desired, one or more filter(s) and/or amicrolens can be fabricated above the uppermost metal layer 532.

FIG. 5AB illustrates a filter 520, such as an inorganic dielectricoptical filter, formed below the slats 112 in a trench. Additionaldetails of how to form such a trench, and form a filter therein, aredescribed in commonly assigned U.S. patent application Ser. No.13/466,867, entitled OPTICAL SENSOR DEVICES INCLUDING FRONT-END-OF-LINE(FEOL) OPTICAL FILTERS AND METHODS FOR FABRICATING OPTICAL SENSORDEVICES, filed May 8, 2012, (Attorney Docket No. ELAN-01266US2), whichis incorporated herein by reference.

The inorganic dielectric materials used to form the dielectric opticalfilter (e.g., 520) can include silicon dioxide (SiO2), silicon hydride(SixHy), silicon nitride (SixNy), silicon oxynitride (SixOzNy), tantalumoxide (TaxOy), gallium arsenide (GaAs), gallium nitride (GaN), and thelike. Alternating layers in the optical filter may have a constant orvarying film thickness throughout the filter stack, in order to achievethe desired optical response. By careful choice of the exactcomposition, thickness, and number of these layers, it is possible totailor the reflectivity and transmissivity of the optical filter toproduce almost any desired spectral characteristics. For example, thefilter can be designed as a long-pass or short-pass filter, a bandpassor notch filter, or a mirror with a specific reflectivity.

The slats 112A, 112B and 112C of the sensors 102A, 102B and 102C wereshow as being generally straight up and down and perpendicular relativeto the surface of the PD regions 104A, 104B and 104C, respectively. Inalternative embodiments, the slats can be slanted such that theyresemble louvers or “venetian blinds”, as will now be described withreference to FIGS. 6A and 6B.

FIG. 6A illustrates a side view of an optical sensor 602A, according toan embodiment of the present invention. The optical sensor 602A includesa PD region 604A above which are located parallel slanted slats 612A,which can also be referred to as louvers 612A. More specifically, thelouvers 612A slant downward from left to right. FIG. 6B illustrates aside view of an optical sensor 602B, according to an embodiment of thepresent invention. The optical sensor 602B includes a PD region 604Babove which are located parallel slanted slats 616B, which can also bereferred to as louvers 612B. More specifically, the louvers 612B slantdownward from right to left. The PD regions 604A and 604B are formed ina semiconductor wafer substrate 606.

The angled slats 612A of the sensor 602A enable the sensor 602A toprimarily detect light have a first angle of incidence, whereas theslats 612B of the sensor 602B enable the sensor 602B to detect lighthaving a second angle of incidence. This enables the sensors 602A and602B to be used together to detect whether an object (that reflectslight from a light source), or a light source, is moving fromleft-to-right relative to the sensors 602A and 602B, or fromright-to-left. Assume a similar configuration to that shown in FIG. 1D,but assume the sensors 602A and 602B are used in-place of the sensors102A and 102B, respectively. If an object that reflects light producedby a light source is moving from the left toward the sensors, then thesensor 602A will produce an earlier and greater response than the sensor602B. Similarly, if a light source is moving from the left toward thesensors (or is to the left of the sensors), then the sensor 602A willproduce an earlier and greater response than the sensor 602B. If anobject that reflects light produce by a light source is moving from theright toward the sensors, then the sensor 602B will produce an earlierand greater response than the sensor 602A. Similarly, if a light sourceis moving from the right toward the sensors (or is to the right of thesensors), then the sensor 602B will produce an earlier and greaterresponse than the sensor 602A.

It is also with the scope of the present invention to include numeroussensors similar to those shown in FIGS. 6A and 6B, with each sensorhaving slats 612 having a different angle than the other sensors, tothereby enable the sensors to collectively be used to detect where anobject that reflects light (or a light source that transmits light) isrelative to the sensors, by comparing the response of the numeroussensors.

Further sensors having slanted slats, similar to those in sensors 602Aand 602B, but having slats orthogonal to those of the sensors 602A and602B can be used together to detect whether an object (that reflectslight from a light source), or a light source, is moving fromfore-to-aft or aft-to-fore.

FIG. 7 illustrates that the slanted slats 612 can be made of metal,during BEOL metallization process steps, from a plurality of metallayers 732, which are connected in a stacked configuration with aplurality of metal columns 734, such as vias, contacts, or tungstenplugs. More specifically, the slanted slats can be made by laterallyoffsetting, by a predetermined lateral spacing, the various metal layers732 and/or columns 734 that are stacked one above the other to make upeach slat. If desired, one or more filter(s) can be fabricated above theuppermost metal layer 732, are below the slats in a trench, as wasdiscussed above with reference to FIGS. 5A and 5B.

Embodiments of the present invention can be used to detect simplegestures such as horizontal left-to-right motion, horizontalright-to-left motion, vertical up-to-down (i.e., fore-to-aft) motion andvertical down-to-up (i.e., aft-to-fore) motion. The detected simplegestures can be used, e.g., to control a parameter (such as volumeand/or brightness) of an electronic device, to move a cursor on ascreen, or to control operation of a video game, but is not limitedthereto.

FIG. 8 is a high level block diagram of a system according to anembodiment of the present invention. Optical sensors of embodiments ofthe present invention can be used in various systems, including, but notlimited to, mobile phones, tablets, personal data assistants, laptopcomputers, netbooks, other handheld-devices, as well asnon-handheld-devices. Referring to the system 800 of FIG. 8, a pluralityof optical sensors (e.g., 102 and/or 602) described herein, collectivelyrepresented by block 802, can be used to control whether a subsystem 806(e.g., a touch-screen, display, backlight, virtual scroll wheel, virtualkeypad, navigation pad, audio speaker etc.) is enabled or disabled, andwhether the brightness, volume or other parameter of the subsystem isincreased, decreased or otherwise modified. Referring to FIG. 8, aprocessor and/or other circuitry 804 (e.g., amplifiers, integrators,ADCs, comparators, subtraction circuitry, etc.) can detect motion and orrelative positions based on responses produced by the optical sensors802, e.g., in order to determine whether a motion or gesture has beendetected that is intended to control the subsystem 806, and theprocessor and/or other circuitry 804 can control the subsystem 806accordingly. The processor and/or other circuitry 804 can also includeregisters and/or memory that is used to store motion and/or positiondetection data. The system can also include a driver 808 configured toselectively drive the light source 122. Such a driver can be part of, orseparate from, the processor and/or other circuitry 804.

FIG. 9 is a high level block diagram that is used to describe methodsaccording to various embodiments of the present invention. Such methodsare for use with one or more first optical sensors each including aphotodetector region and a plurality of first slats over thephotodetector region, and one or more second optical sensors eachincluding a photodetector region and a plurality of second slats overthe photodetector region, wherein the second slats have a differentconfiguration than the first slats. Exemplary optical sensors that canbe used for such methods were described above with reference to FIGS.1-8. For example, as was described above, the second slats can beorthogonal relative to the first slats. Additionally, or alternatively,the first slats can slant in a first direction, and the second slats canslant in a second direction generally opposite the first direction.Referring to FIG. 9, at step 902, the first optical sensor(s) and thesecond optical sensor(s) are used produce currents indicative of lightincident on the optical sensors. At steps 904 and/or 906, the currentsproduced at step 902 are used to distinguish between movement in atleast two different directions and/or determine a position of oneelement of relative to another element. At step 908, the results ofsteps 904 and/or 906 are used to control a subsystem.

The foregoing description is of the preferred embodiments of the presentinvention. These embodiments have been provided for the purposes ofillustration and description, but are not intended to be exhaustive orto limit the invention to the precise forms disclosed. Manymodifications and variations will be apparent to a practitioner skilledin the art.

Embodiments were chosen and described in order to best describe theprinciples of the invention and its practical application, therebyenabling others skilled in the art to understand the invention. Slightmodifications and variations are believed to be within the spirit andscope of the present invention. It is intended that the scope of theinvention be defined by the following claims and their equivalents.

What is claimed is:
 1. An optical sensor, comprising: a semiconductorwafer substrate; a photodetector region formed in the semiconductorwafer substrate; and a plurality of slats formed over the photodetectorregion such that light that is incident on the optical sensor passes bythe slats before reaching the photodetector region; wherein the slatsare made of an opaque polymer material.
 2. The optical sensor of claim1, wherein the opaque polymer material of which the slats are madecomprises an opaque photoresist.
 3. The optical sensor of claim 1,wherein the slats are parallel to one another.
 4. The optical sensor ofclaim 1, wherein the slats are slanted relative to a surface of thephotodetector region.
 5. The optical sensor of claim 1, wherein a firstsubset of the slats crisscross a second subset of the slats, whereineach of the first and second subsets of the slats include a plurality ofthe slats.
 6. The optical sensor of claim 1, further comprising anoptical filter above the slats.
 7. The optical sensor of claim 6,wherein the optical filter is configured to reject infrared light. 8.The optical sensor of claim 6, wherein the optical filter is configuredto reject visible light and pass infrared light.
 9. The optical sensorof claim 1, further comprising an optical filter between the slats andthe photodetector region.
 10. The optical sensor of claim 9, wherein theoptical filter is configured to reject infrared light.
 12. The opticalsensor of claim 9, wherein the optical filter is configured to rejectvisible light and pass infrared light.
 13. An optical sensor,comprising: a semiconductor wafer substrate; a photodetector regionformed in the semiconductor wafer substrate; and a plurality of slatsformed over the photodetector region such that light that is incident onthe optical sensor passes by the slats before reaching the photodetectorregion; wherein the slats are slanted relative to a surface of thephotodetector region.
 14. The optical sensor of claim 13, wherein theslats are parallel to one another.
 15. The optical sensor of claim 13,further comprising an optical filter above the slats.
 16. The opticalsensor of claim 15, wherein the optical filter is configured to rejectinfrared light.
 17. The optical sensor of claim 15, wherein the opticalfilter is configured to reject visible light and pass infrared light.18. The optical sensor of claim 13, further comprising an optical filterbetween the slats and the photodetector region.
 19. The optical sensorof claim 18, wherein the optical filter is configured to reject infraredlight.
 20. The optical sensor of claim 18, wherein the optical filter isconfigured to reject visible light and pass infrared light.